xen: add "capabilities" file

The xenfs capabilities file allows usermode to determine what
capabilities the domain has.  The only one at present is "control_d"
in a privileged domain.

Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>

1 files changed, 18 insertions, 1 deletions

diff --git a/drivers/xen/xenfs/super.c b/drivers/xen/xenfs/super.c
index 515741a8e6b8..6559e0c752ce 100644
--- a/drivers/xen/xenfs/super.c
+++ b/drivers/xen/xenfs/super.c
@@ -20,10 +20,27 @@
 MODULE_DESCRIPTION("Xen filesystem");
 MODULE_LICENSE("GPL");
 
+static ssize_t capabilities_read(struct file *file, char __user *buf,
+                                 size_t size, loff_t *off)
+{
+        char *tmp = "";
+
+        if (xen_initial_domain())
+                tmp = "control_d\n";
+
+        return simple_read_from_buffer(buf, size, off, tmp, strlen(tmp));
+}
+
+static const struct file_operations capabilities_file_ops = {
+        .read = capabilities_read,
+};
+
 static int xenfs_fill_super(struct super_block *sb, void *data, int silent)
 {
         static struct tree_descr xenfs_files[] = {
-                [2] = {"xenbus", &xenbus_file_ops, S_IRUSR|S_IWUSR},
+                [1] = {},
+                { "xenbus", &xenbus_file_ops, S_IRUSR|S_IWUSR },
+                { "capabilities", &capabilities_file_ops, S_IRUGO },
                 {""},
         };